Semiconductor devices reside in many electrical products to operate as resistors, capacitors, transistors, memory cells, and other components. A typical semiconductor device has many surface structures formed above a substrate and many active regions formed within the substrate. The surface structures and the active regions act together to form the function of the semiconductor device.
A dielectric layer is usually blanketed over the surface structures and the substrate to insulate them from other circuit layers within the semiconductor device. Glass is usually the material for this kind of dielectric layer.
During manufacturing, the glass layer (dielectric layer) is first deposited. Next, a reflow (melting) process is performed to flatten the surface of the glass layer. Today, the glass is usually doped with materials such as boron and phosphorous (dopants) to reduce the temperature of the reflow process. Thus, a doped glass has one or more dopant materials. The dopant in the doped glass, however, tends to diffuse outward and migrate to the surface structures and the substrate. This outward diffusion may change the electrical properties of the surface structures, the active regions in the substrate, the substrate itself, and hence, the performance of the device.
Most devices now have a barrier layer sandwiched between the doped glass layer and the surface structures to prevent the migration of the dopant from the doped glass layer to the surface structures and the substrate.
Silicon nitride has been suggested as the material for the barrier layer. However, the device formed by the surface structures and the active regions may suffer from underalloy due to hydrogen blocking properties. Static retention time may decrease when silicon nitride is used on a silicon substrate. This may be caused by stress, interface build up, or fixed charge.
Further, today, with increasing aspect ratio (depth to width ratio) of the gaps between the surface structures (for example, narrower gaps), the barrier layer is limited to a certain layer thickness in these gaps. With this layer thickness limitation, silicon nitride and other tetraethooxysilane (TEOS) materials may not be thick enough to prevent the outward diffusion of the dopant in the doped glass.
Thus, there is a need for an alternative barrier layer.